SAO PAULO, Brazil (AFP) — Half of Brazil’s greenhouse gas emissions come from cattle ranchers clearing Amazon jungle for pasture, and from their herds passing methane, a new study prepared for the Copenhagen climate summit say.

The report was written by 10 Brazilian university researchers and is referenced on the Brazilian government National Institute for Space Research website.

It estimates that between 2003 and 2008, the ranchers produced between 812 million and 1.1 billion tonnes of carbon gases a year, or 50 per cent of the national total.

Most came from the slash-and-burn technique they use to clear vast areas of the Amazon jungle for short-lived pastures, but cow burps and flatulence also contributed, the study said.

Although those factors were already generally well known, this is the first time the environmental impact of Brazil’s huge beef industry has been quantified.

The report said cattle farmers accounted for at least 75 per cent of Amazon deforestation, ahead of rice farmers and urban encroachment.

The study noted a decline in the amount of annual greenhouse gases caused by cattle activities over the period studied.

But in 2008, emissions still amounted to 813 million tonnes, most of it from the Amazon, though some also came from the Cerrado scrub farther south in inland Brazil, it said.

The report’s authors suggested limiting the amount of carbon produced by ranchers by genetically altering cattle so that more could be squeezed on to each pasture, reducing the amount of land required, while maintaining beef yields.

Currently, 300 kilogrammes (660 pounds) of carbon is emitted for each kilogramme (2.2 pounds) of beef produced in Brazil.

Brazil is offering to reduce carbon emissions by 36 to 39 per cent, based on projected 2020 levels, largely through reducing Amazon deforestation.

On Friday, though, the daily Folha de S Paulo reported that President Luiz Inacio Lula da Silva had declared an amnesty for landowners fined for over-clearing their land of native vegetation — including those wiping out parts of the Amazon.

The decree, announced in the official government gazette, meant that six-billion-dollar worth of fines would be forgiven, the newspaper said.